The clinical anatomy of the communications between the radial and ulnar nerves on the dorsal surface of the hand.

Sensations of the dorsal surface of the hand are supplied by the radial and ulnar nerves with the boundary between these two nerves classically being the midline of the fourth digit. Overlap and variations of this division exist and a communicating branch (RUCB) between the radial and ulnar nerves could potentially explain variations in the sensory examination of the dorsal hand. The aim of this study was to examine the origin and distribution of the RUCB thereby providing information that may potentially decrease iatrogenic injury to this connection. We grossly examined 200 formalin-fixed adult human hands. A RUCB was found to be present in 120 hands (60%). Of the specimens with RUCBs, we were able to identify four notable types. Type I (71, 59.1%) originated proximally from the radial nerve and proceeded distally to join the ulnar nerve. Type II (23, 19.1%) originated proximally from the ulnar nerve and proceeded distally to join the radial nerve. Type III (4, 3.3%) traveled perpendicularly between the radial and ulnar nerves so that it was not possible to determine which nerve served as its point of origin. Type IV (18.3%) had multiple RUCBs arising from both the radial and ulnar nerves. With the continual development of new surgical techniques and the ongoing effort to decrease postoperative complications, it is hoped that this study will provide useful information to both anatomists and surgeons.